Piezo Actuator Gas Jacket for Dielectric Protection
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Solution Overview
Problem
Piezo-electric actuators in fuel injectors fail due to short circuits from electrochemical ion migration, surface flash-over, and reduction of insulating lead oxide in Lead Zirconate Titanate (PZT) materials, exacerbated by water and hydrogen contamination, which cannot be completely eliminated during manufacturing.
Innovation Solution
Encapsulating a piezo-electric actuator within a gas jacket at pressures above atmospheric pressure, with a low-permeability, flexible encapsulation and a hermetically sealable gas connection, containing chemically active substances to react with water and hydrogen, and using Oxygen or dry air to oxidize lead formations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the piezo-electric actuator is operated in a pressurised gas environment, then the dielectric strength increases and failure modes are reduced, but the device complexity increases due to the need for encapsulation and gas management systems
Solution Approach 1:
The piezo-electric element is nested within an encapsulation that contains a pressurised gas environment. This nested structure allows the actuator to operate in a controlled atmosphere that enhances reliability while containing the complexity within a compact hierarchical arrangement.
Solution Approach 2:
The actuator operates in a pressurised gas environment that creates an inert or controlled atmosphere, preventing electrochemical ion migration and surface flash-over failures. The gas pressure maintains dielectric strength and prevents contamination while isolating the actuator from harmful external environments.
2Temperature
If a gas jacket surrounds the piezo-electric element, then heat dissipation improves, but the volume of the actuator increases
Solution Approach 1:
A gas jacket surrounds the piezo-electric element to provide thermal management through gas circulation and convection. The gas medium efficiently conducts heat away from the actuator while maintaining a compact structure, leveraging pneumatic principles for thermal control without requiring large heat sinks.
3Object-affected harmful factors
If the encapsulation is made impermeable, then fluid ingress is prevented, but the manufacturing complexity and sealing requirements increase
Solution Approach 1:
The encapsulation creates a hermetic seal that establishes an inert, dry environment around the piezo-electric element. This prevents water and hydrogen ingress that would cause electrochemical failures, while the sealed environment allows for controlled filling with dry gas during manufacturing.
Solution Approach 2:
A desiccant or chemical drying agent is placed within the encapsulation as an intermediary substance to actively absorb any residual moisture. This provides an additional layer of protection against fluid ingress while allowing the encapsulation structure itself to be simpler.
4Reliability
If passivation layers are applied to exposed electrodes, then short circuit failures are prevented, but the manufacturing complexity and material requirements increase
Solution Approach 1:
The pressurised gas environment serves as a protective atmosphere that eliminates the need for complex passivation layers. The high dielectric strength and controlled chemistry of the gas environment prevent electrochemical ion migration and surface flash-over, allowing electrodes to remain exposed while maintaining reliability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution reduces failure modes by enhancing dielectric strength, heat dissipation, and fluid migration, while maintaining a dry environment within the actuator, effectively preventing short circuits and surface contamination, and ensuring reliable operation.
Implementation Method 1
the dielectric strength of gasses increases with their pressure
Implementation Method 2
the thermal conductivity of the gas is increased when it is pressurised which enables the gas to better dissipate the heat generated by the piezo-electric element
Implementation Method 3
as the gas will be circulated within the encapsulation by convection currents any damaging fluids on the surface of the piezo-electric element will be distributed within the gas
Implementation Method 4
a chemically active substance is provided inside the encapsulation, wherein, in use, the substance chemically combines with water to form a compound
Implementation Method 5
Hydrogen can be stored in a metal hydride form
Implementation Method 6
Oxygen or dry air to oxidize lead formations
Data Source
Figure 1
Figure 2
AI summary
A piezo-electric actuator (1) for use in a diesel engine. The actuator (1) comprises a piezo-electric element (3) which is encapsulated such that a layer of gas at a pressure above atmospheric pressure surrounds the piezo-electric element. The presence of the gas within the encapsulation around the element (3) avoids the need to passivate electrodes exposed on the surface of the element.